My invention relates to a pipe at least on a part of its length provided with an outer foam plastic layer which on its outside is wrapped with a surface layer consisting of windings of thermoplastic tape partially overlapping each other, the overlapping parts being sealed to each other.
Such a known pipe having over a part of the length an outer polyurethan foam plastic layer which on its turn is wrapped on its outside with a polyethylene covering layer is obtained by wrapping the polyurethan layer at the temperature of extrusion with polyethylene tape issuing from the extruder, the overlapping parts of the tape being automatically heatsealed to each other.
Also pipes are known in which a thermoplastic tape which at normal temperature is wrapped around the foam plastic layer, whereupon the overlapping parts are heatsealed to each other by means of a heatsealing tool.
These pipes are advantageous in that due to the presence of the foam plastic layer a great floating power can be imparted thereto whereby such pipes may be used as floating pipes in dredging operations. In that case preferably an inner pipe is used consisting of fibre reinforced plastic, like glass fibre reinforced polyester- or epoxy pipe. Obviously it is also possible to use metal pipes to which a floating power is imparted by means of the foam plastic layer.
On the other hand the foam plastic layer can serve as insulating material for a pipe, particularly a metal pipe, which is particularly of importance in conveying warm fluids, like heated hydrocarbon products or cooled hydrocarbon products, e.g. liquefied natural gas products, through such a pipe. Although these pipes in practice are satisfactory and can be economically manufactured, since it is sure that a reliable sealed joint is formed by using a polyethylene tape issuing from an extruder, such pipes have the drawback that in case of damages, as e.g. owing to collisions of such pipes as used as floating pipes in dredging operations with boats, or, in installing the pipes in the ground, owing to sharp objects, like sharp stones, this damage causes a lengthwise extending crack, whereby the whole wrapping of the pipe loosens and gets lost, so that the foam plastic becomes uncovered.
In floating pipe bodies as used in dredging now the waves cause a fast corrosion of the foam plastic layer, whereby after a short time the buoyancy of the pipe is lost and a new pipe should be provided.
In the case of pipes installed in the ground the problem occurs that water can penetrate into the foam plastic layer, when the covering layer is damaged involving a decrease of the insulating power considerably.